1. Field of the Invention
The invention relates to a process for machining a wafer-like workpiece between two plates of a machining tool. The invention relates in particular to material-removing machining of a semiconductor wafer in a polishing or lapping machine.
2. The Prior Art
When semiconductor wafers are polished, a distinction is drawn between double-side polishing and single-side polishing. The machines used for this purpose are commercially available and are distinguished in particular through the fact that in single-side polishing there is a carrier plate, to which the workpiece is fixed, instead of an upper working wheel covered with polishing cloth. In double-side polishing and lapping, by contrast, there are two working wheels, between which the workpiece is machined, the working wheels only being covered with polishing cloth in the case of double-side polishing. The workpiece is held in a dedicated cutout in a template between the working wheels.
Furthermore, a distinction can be drawn between single-wafer machining and multi-wafer machining, depending on whether one workpiece or a plurality of workpieces simultaneously is/are machined. Due to the high throughputs which can be achieved, the lapping and polishing of semiconductor wafers is generally carried out as multi-wafer machining. The present invention is suitable for both single-wafer machining and multi-wafer machining.
To ensure the desired effect of removing material and improving the flatness of the workpiece, a lapping abrasive is supplied to the workpiece during lapping and a polishing abrasive is supplied to the workpiece during polishing, and the workpiece is acted on by a pressure. The pressure is usually transmitted via a pneumatic, hydraulic or electrical force-transmitting device which presses the upper working wheel or the carrier plate onto the lower working wheel and the workpiece located between them. During the lapping or polishing of the workpiece, at least one of the working wheels or at least the carrier plate is rotated about its center.
Japanese Patent No. JP-05177534 A proposes a process for polishing semiconductor wafers which has an optimized throughput and in which polishing is initially carried out at a relatively high polishing pressure, in order to achieve a high level of material removal, while toward the end of the polishing the polishing pressure is reduced considerably in order to improve the flatness of the polished semiconductor wafers.
The present invention provides a process for the material-removing machining of planar workpieces with which particularly planar workpieces are obtainable at high throughputs.
The invention relates to a process for machining a wafer-like workpiece between two plates, in which material is abraded from the workpiece under the influence of an auxiliary substance supplied and of a pressure acting on the workpiece, wherein the pressure on the workpiece is significantly reduced and then increased again at least once during the machining of the workpiece, and the supply of the auxiliary substance is reduced as the pressure is increased.
The process is suitable for the material-removing machining of wafer-like workpieces of all types, but in particular for the lapping or polishing of semiconductor wafers which consist, for example, of silicon or of compound semiconductors.